1. Technical Field
The present invention relates to apparatuses, systems, and methods for reaming or otherwise producing a borehole within a workpiece, and more particularly, to an apparatus for producing a finished borehole in a single pass, wherein said apparatus includes a cutting tool, and a compressible element configured to laterally support the tool and engage the workpiece, during the boring process.
2. Background Art
In the automotive industry, methods of manufacturing cylinder heads play important roles in determining the overall cost of producing an internal combustion engine. The heads perform the important primary function of providing passageways for sufficient fuel and air to enter into a plurality of combustion chambers cooperatively defined by the heads, pistons, and cylinders of the engine. As such, each head typically presents an integrated body that defines a plurality of passageways (or boreholes). Each passageway is specifically configured to house a valve stem, so as to cyclically control the ingress and egress of fuel, air and exhaust. More particularly, these passageways include valve-guides and valve seats, wherein the oscillating valve stems are caused to translate.
Conventional processes have been developed for efficiently producing finished valve guides, and meeting the tolerances necessary to achieve desired performance. On a mass scale, these processes typically include automated three-dimensional work cells and robotic operation for manipulating rough dies (or workpieces) produced from raw material, such as aluminum or steel. Automated sub-routines are provided for performing various cutting and boring functions necessary to produce the finished valve guide boreholes in the workpiece within specified controls (e.g., 60.010 mm, perfect straightness, and maximum runout of 0.080 mm to the seat, etc.). These sub-routines typically employ a Computer Numerical Control (CNC) machine to provide a precision cutting, programmable and flexible machining process. The CNC machine is typically used in conjunction with standard reamer tools to finish the valve guides, which are typically pre-formed by a powder metallurgy process and pressed into the workpiece.
The sub-routines and processes used for machining the finished valve guides, however, present various cost inefficiencies and concerns. In order to produce a production quality hole, a plurality of passes, including a first pass wherein a smaller diameter tool is used to create a pilot (or starter) bore through a fraction of the workpiece depth, and a second finishing pass wherein the finishing tool is used to produce the final bore through the full workpiece depth, must be utilized to avoid unacceptable eccentricities caused by lateral tool deflection. Though, the pilot bore minimizes deflection during the finishing application, its implementation adds to the overall production time, and labor/energy costs. The addition of a second tool and accompanying redundant mechanisms result in a reduction of available workspace, a more complex process, and the need for greater repair and inventory capacity.
Conventional squirt-reamer single-pass processes have been developed to address these concerns. More particularly, these conventional single-pass systems are typically used with transfer line equipment or equipment dedicated to a single or limited number of uses, and incorporate a dedicated fourth axis concentrically aligned with the spindle to pilot the tool through a bushing. The bushing is fixedly secured relative to the spindle and tool holder. In operation, the bushing is positioned against the workpiece at the entrance of the bore, so as to laterally support the tool as it translates. It is appreciated that providing lateral support during the boring process controls tool straightness, reduces the eccentricity of the borehole, and limits runout relative to the valve-seat.
Squirt-reaming systems, however, present configuration and efficiency concerns that make them incompatible with CNC machining processes, and therefore unsuitable for mass-producing machined boreholes in typical cylinder head environments. First, squirt-reaming systems cannot be used with CNC machines due to a lack of flexibility with the tool change system. Conventional CNC machines are not configured to perform the necessary tool translations relative to the machining apparatus, and as such, would require substantial modifications to perform in this manner. Finally, it is also appreciated that incorporating the complex mechanical designs of conventional squirt reaming systems in a CNC machining process would result in higher susceptibility to failures, more maintenance for the station, and lower productivity.
Thus, there is a need in the art for a single-pass finished bore machining system that is suitable for mass producing ported cylinder heads.